squeak, sorry but i believe you are wrong there...most of these keyboards can actually send out the arp/arranger info via the midi out..they usually have a software RX/TX midi data somewhere in the system menus... in effect all the minimo would be used for would be generating the patterns, none of the voices, and whislt the s90es would be used as the controlling keyboard the ES sound engine would also be used (128 note poly) so poly is not an issue....that is of course unless yamaha make it deliberately not available to the midi out..
cheers